1. Technical Field
The present disclosure relates to the field of radiation therapy treatment planning, and, more particularly, to a system and a computer-implemented method for beam weight optimization that includes population-based heuristics, population-based meta-heuristics, memes, local search, and/or local or global learning procedures.
2. Description of Related Art
Radiotherapy is a technique of treating tumors within a patient using beams of ionizing radiation. An objective in a radiotherapy procedure is to deliver a desired dose of radiation to a targeted tumor volume while limiting the amount of radiation received by surrounding tissue. This is accomplished by directing a series of radiation beams into a patient from different directions whereby the locus of the series of beams coincides with the tumor volume. While the surrounding tissue along the path of a beam may receive only a small fraction of the radiation dose, the tumor located at the intersection of the series of beams receives a much greater aggregate radiation dose.
The properties of the series of beams, e.g., the number, angle, intensity, aperture, and duration thereof is referred to in the art as a treatment plan. One objective of a treatment plan is to minimize the amount of radiation received by vital organs which may be located near the target tumor while delivering a prescribed radiation dose to the tumor. Such organs may be referred to as organs at risk (OAR). When preparing a treatment plan it must also be considered which, if any, of the surrounding organs have an increased sensitivity to radiation damage when compared to other organs in the treatment field. Surgical implants, such as and without limitation, internal bone fixations or cardiac pacemakers, may also be considered. Thus, another objective of a treatment plan is to ensure the amount of radiation received by particularly radiosensitive organs adjacent to the targeted tumor is limited to a dose lower than that where damage or undesirable side effects may occur.
Treatment planning methodologies fall broadly within two recognized types: forward planning, and inverse planning. Forward planning is a generally manual process whereby the practitioner empirically determines the treatment plan based on the dose to be delivered to the tumor, and thereafter identifies as a side-effect the collateral dose imposed on surrounding tissue and organs. Inverse planning is a computer-executed process whereby a practitioner specifies dose-volume constraints as input to an inverse planning algorithm, which is then executed on a processor to develop a treatment plan. Dose-volume constraints may include a target volume, minimum and maximum doses to be delivered to the target to achieve a therapeutic objective, and dose-volume limits to be delivered to surrounding tissues and organs. During inverse planning, non-targeted organs and/or tissue may be assigned a weighting factor related to the sensitivity of the non-targeted organs and/or tissue to radiation, which is taken into account while arriving at a suitable treatment plan.
The quality of a treatment plan may be assessed in part by its dose homogeneity, which is defined as the uniformity of radiation dose throughout the targeted tumor volume, and by its conformality, which is defined as the degree to which the delivered radiation dose conforms to the size and shape of the target tumor, e.g., the planning treatment volume, or PTV. Known inverse planning algorithms may be computationally intensive, and even using current processors such as an Intel® Core™ 2 Duo Processor, a treatment plan may take hours to develop.
In standard radiotherapy treatment delivery, a radiation source is mounted on a gantry capable of rotation in a single plane about a fixed point of rotation known as the isocenter. In a type of radiotherapy known as Intensity Modulated Radiation Therapy (IMRT), a “step and shoot” or “sliding window” approach is employed wherein the radiation source is placed in a fixed position in accordance with the treatment plan, the beam is activated for a prescribed duration and then deactivated, and the radiation source is repositioned while deactivated as it is being repositioned for the next beam. In another type of radiotherapy known as Intensity Modulated Arc Therapy (IMAT), a “moving beam” paradigm is employed wherein during an activation period the beam is moved through an arc centered around the tumor volume.
In robotic radiotherapy, a radiation source is mounted on a robotic arm. The radiation source and robotic arm are controlled by a computer programmed to position and activate the radiation source within a range of angles and intensities during treatment in accordance with a predetermined treatment plan.
A treatment planning method that provides improved homogeneity and conformality, reduced exposure of surrounding tissue to undesirable radiation, with reduced computational requirements would be a welcomed advance.